Talking Durometer—Bushing 101 with Energy Suspension

There are a lot of things on our cars that seem simple but are, in actuality, very complicated. Take for example, bushings. Your average driver wouldn’t have any clue what bushings are in relation to the car, what they do, or what they are made of. Your average performance enthusiast is probably better versed in the subject, but probably still only understands the basics of, “Poly bushings are a good upgrade for street cars. Racecars use solid bushings.” So we thought we’d sit down with our friends at Energy Suspension and try and shed some light on polyurethane bushings and why they are a worthwhile upgrade.

Polyur-e-what?

Some of Energy Suspension’s replacement parts utilize factory metal mounting pieces, and only replace a portion of the factory mount. Others might have metal mounting hardware permanently molded into the piece.

Let’s start at the beginning. From the factory, all vehicles come with bushings at various points in the car. Generally they are used where something that moves is mounted to something else that doesn’t move—or at least not in the same direction. The original equipment manufacturer (OEM) bushings are mostly made of soft rubber and allow deflection of the moving parts, which cushions its movements. This is done to keep the ride soft and quiet. OEMs use tests to measure something called NVH or Noise, Vibration, and Harshness—basically the “comfort” of a car. Since soft rubber is the most compliant of the materials, it’s often used, at the cost of high deflection. In a performance application, this deflection is wasted motion, which results in “loose” handling and wasted ET.

One area where Energy shines is getting complete bushing kits to market fast. If you’re going through the trouble of replacing a couple bushings, why not do them all? These complete kits make it easy.

Purpose-built racecars often use specially designed solid bushings called heim joints (or in some production-car-turned-racecar applications, bushings made of metal that replace OEM bushings are used) that allow next to no deflection and pass along every movement, bump, and vibration they encounter. That is great for performance, but not great for comfort. Enter polyurethane performance bushings, the hallowed middle ground.

This is a durometer tester. The small point at the base is specific to the “Shore A” durometer it is calibrated for. The “A” scale isn’t just a measurement range, but also a testing protocol.

Polyurethane is a polymer that is much firmer than rubber, and offers greatly reduced deflection, but is still “soft” enough to retain some NVH dampening characteristics. Lately, there have been some incredible performances from racers using polyurethane bushings, proving that they work on street cars as well as really fast street cars. Of course, none of this is new. Energy Suspension has been at the forefront of polyurethane performance bushings for over 30 years. The company practices and applies its knowledge of materials science all day every day since it’s the only thing the company does. From muscle cars to sport compacts. Street cars to racecars of all disciplines, Energy Suspension has had experience with them all, and continues to R&D new formulas, new designs, and put out new kits.

A is for Apple.

So, if polyurethane is harder than rubber, but softer than steel, how do we quantify that? Can it be measured? The answer to that is, yes! The hardness of polyurethane and rubber are measured in units called “durometer”. Now a quick intro on measuring durometer, as it is a science in and of itself. There are a number of “scales” Shore Durometer is measured by. Each scale has a different firmness range that it measures (with some overlap between similar scales) and a different test method. For the purposes of this article, most of the durometer measurements talked about will be “A Shore” measurements.

You can see the range of options and their differences in this graph. You can also see the relationship between NVH transmission and performance of the bushings.

Choosing the right durometer polyurethane for the right application is crucial to achieving maximum performance while still generating a tolerable ride on the street. We asked Jamey Spaeth, Energy Suspension’s Engineering Project manager how the company determines the right durometer for the right application.

“Choosing the correct durometer is based on three primary factors: The type of bushing, the vehicle application, and empirical knowledge. Knowing what purpose the bushing serves helps us determine what durometer will deliver the performance we expect,” explained Spaeth. “Second, the application helps us determine how much force and stress the bushing will see when in use. Lastly, since Energy Suspension has been in business for thirty-plus years, we have the luxury of looking back on the development of our past bushings and identifying what durometers have worked best in a given application.”

As he explains it, there is some art to the science of spec’ing the right material for the right jobs. Energy has materials in a wide range of durometers at its disposal.

“We typically manufacture bushings with a durometer ranging from 62 Shore A up to 70 Shore D, which is about equivalent to 120 Shore A,” Spaeth explained. “We’re continually developing new materials and formulations, so that range can always extend if it is required by a particular application.”

This is an OEM rubber bushing. You can see how much it deflects even with simple hand strength. In addition to better performance, polyurethane bushings also have up to ten times the lifespan of rubber bushings.

Generally a single durometer is offered for a single application—there aren’t “soft,” “medium,” and “hard” bushings available for your stock control arms and the general rule of thumb is said to be that polyurethane bushings last about 10 times longer than the rubber bushing they replace, which means that in all but the most extreme applications, they never have to be replaced. For those of you wondering, the two main colors offered by Energy—black and red—are exactly the same except for the color.

Here, a bushing is being tested for Shore A durometer, and is measuring “79A”—significantly firmer than rubber.

With constant R&D going on and advancements in materials sciences being made, polyurethane bushings are becoming more and more capable in extreme performance applications, and less of a “compromise” on street cars. Whether you have a weekend cruiser or an eight-second True Street car, chances are, polyurethane bushings are going to help your car in one way or another.